1. Field of the Invention
This invention relates to a molding machine and a molding method for press-molding molten glass flowing out of a glass melting furnace to form glass optical element.
2. Description of the Related Art
Examples of the conventional methods for forming a glass optical element are Japanese Patent Laid-Open Publication No.3-45523 (hereinafter referred to as Publication 1), Japanese Patent Publication No.61-38130 (hereinafter referred to as Publication 2), Japanese Patent Publication No.63-37044 (hereinafter referred to as Publication 3), Japanese Patent Publication No.55-15420 (hereinafter referred to as Publication 4), Japanese Patent Publication No.3-72016 (hereinafter referred to as Publication 5), and the publication of U.S. Pat. No. 5,087,279 (hereinafter referred to as Publication 6).
The technical contents of these publications are as described below.
The following is the technical content described in Publication 1:
A method of manufacturing an optical glass element including:
(1) a step of receiving molten glass by a first heating jig; PA1 (2) a step of transporting the molten glass by inverting the molten glass on a second heating jig while the molten glass is adhered to the second heating jig; PA1 (3) a step of forming an optical glass molded piece by thermal deformation on the second heating jig; and PA1 (4) a step of heating and press-molding the optical glass molded piece by a pressing mold. PA1 (1) molding a glass piece obtained by cutting a lump of molten glass by using a preliminary molding mold to obtain a preliminarily-molded glass piece; PA1 (2) extracting this glass piece out of the preliminary molding mold by attracting an upper surface portion of the glass piece while a central portion of the glass piece is in a softened state; PA1 (3) heating the glass piece so that glass piece has a viscosity such that it can be press-molded; PA1 (4) heating and press-molding the attracted surface of the glass piece.
In this method, molten glass is received by the first heating jig maintained at a comparatively low temperature and is thereafter attached to the second heating jig and inverted. The optical glass is deformed by heat with its creased surface facing upward to remove a crease-like defect in the surface which has contacted the heating jig.
The following is the technical content described in Publication 2:
A method of molding a thick optical glass molded article by press molding including:
supplying the glass piece to a pressing mold by stopping the attraction; and
According to this method, a glass piece can be molded in a state where the temperature of a central portion of the glass piece is substantially equal to or lower than the temperature of an outer peripheral portion, and is at a low temperature in a molding temperature range. It is thereby possible to obtain a molded article free from any sink mark and having an improved appearance.
The technical content described in Publication 3 resides in transporting a preform or glass molded piece between molding sections by supporting the molded piece on a ring-like barrel mold. That is, a glass transporting method is described in which sections for preheating, uniform heating, press molding, cooling and introduction/extraction are disposed concentrically, a pinching device provided at the center of the molding sections is rotated in a tact-rotation manner and extended and retracted in the direction of each section to successively transport preforms or glass molded pieces to form a pressed lens. In this method, a ring-like barrel mold serving as a barrel mold of a mold assembly for the press molding section and having in its outer circumferential surface a pinching portion in which the pinching device is inserted is moved with respect to the sections while internally supporting the preforms or press molded pieces.
The technical content described in Publication 4 is a method of supplying a deformable high-temperature glass piece to a lower mold part in a barrel mold to mold an optical element, wherein each one of a number of deformable heated glass pieces varying in volume is formed into a partially molded glass piece having an accurate predetermined volume to be continuously and efficiently molded into a molded piece having a complete predetermined shape.
The technical content described in Publication 5 is a method of molding an optical member including a step of preparing a glass solution, a step of controlling the temperature of a mold, a first pressing step of pressing the glass into an approximate shape having a predetermined thickness, and a second pressing step of pressing the glass while convergently controlling the mold temperature, and a glass cooling step.
The technical content of Publication 6 corresponds to the application filed as a combination of the application of the content of Publication 1 and other two applications (Japanese Patent Application Nos. 1-195061 and 1-280976), and is basically the same as the above-described technical content described in Publication 1.
There are problems described below with respect to the above-described conventional art.
With respect to Publication 1, the period of time through which the molten glass contacts the second heating jig, which is a lower mold part for molding into a finished shape is very long since thermal deformation is caused on the second heating jig. The molding cycle time is therefore long resulting in a low productivity in mass production. To improve the productivity, the production cost at an initial stage (initial cost) must be increased.
In the case of the method of Publication 2, in the step of extracting the glass piece from the preliminary molding mold by attracting an upper surface portion of the glass piece, the attracted surface is cooled by an attraction cylinder, so that the time taken to reheat the attracted surface is considerably long. A problem in terms of productivity is therefore encountered. Also, a defect in appearance can occur easily because of the method of directly attracting an optical surface.
In the transport method of Publication 3, a preform which is a solidified glass raw material is supplied to a supporting portion of the ring-like barrel mold. In the case of a method of obtaining a molded piece by using molten glass as a glass raw material, it is difficult to supply molten glass having a certain viscosity and to transport the same between the heating and molding sections.
In the method of Publication 4, pre-molding is performed on a first upper mold part and the molded piece is thereafter heated and is molded into an optical element on a second upper mold part. However, no means or step of separating the barrel mold and the lower mold is described.
In the method of Publication 5, pre-molding is performed before molding into an optical element so as to set a 1% or more thickness. However, the mold for the pre-molding is the same as that used to mold the optical element, and the pre-molded glass is not transported by any supporting member.
The method of Publication 6 entails substantially the same problem as the method of Publication 1.